For starters, that’s no email. No Amazon. No Netflix. Even worse, the shipping industry shuts down. Grocery shelves are not restocked. All planes grounded. The economy grinding to a standstill.

If this lasted even for a few days, the country would come to a halt. Massive food shortages would result. Panicked citizens would make a run on banks. ATMs would stop working. The stock market would crash. Gas stations would run dry. Trillions of dollars of investments would vanish in an instant. The country would be thrust into an immediate depression, if not a total economic collapse. To function, we would have to go back to paper and pencil — the modern equivalent of the stone ages.

What could cause such a calamity? A coordinated terrorist attack against the underlying physical architecture that makes the tech world run.

When most people hear about cyberattacks, they remember the 40 million credit cards stolen from Target or Internet viruses like Heartbleed that create vulnerabilities in secure websites. For the average American, the issue only exists when they are personally affected; with companies or banks accountable for our personal information and guarantees of reimbursement for fraudulent behavior, the concern seems far removed. However, the truth about cyberattacks is much more frightening.

Infrastructure is commonly thought of in terms of roads, bridges, and water pipelines — very concrete things. When we use the Internet however, our data is transmitted along a different type of infrastructure. The datacenters, exchanges, and cables that make up our cyber infrastructure are as much a critical component of our national infrastructure as are our roads and bridges. They are, however, out of sight, and for most, this means that they are out of mind.

In spite of the redundancies built into the cyber infrastructure, we have done very little to secure it against the catastrophic risk of a physical attack.

Over the last 20 years, our entire economy has become intertwined with the Internet. From our 911 emergency systems to traffic lights to military command centers, almost nothing used on a daily basis is unconnected. Over the past 10 years, commerce over the Internet has multiplied exponentially — from $93 billion in 2003 to $332 billion in 2013.

So what are we, as a nation, doing to make sure the engine keeps running? The answer is, unfortunately, not much. To the extent that we are doing anything, we focus on securing our Internet from the threat of cyberattacks from non-state actors or countries like China. This does nothing, however, to secure the physical components of our data infrastructure.

While the Obama administration has started to develop oversight on this, we do not yet have a comprehensive plan for securing the switches, datacenters, and cabling that form the backbone of our national economy. No national standards have been developed, and there has been only a few things put out by the Obama administration in terms of government regulation or oversight. What security measures do exist are driven only by the economic interests of the companies that manufacture and maintain equipment they have under their own control. This protection is precarious and piecemeal at best.

As a nation, we need to start taking a hard look at securing this critical infrastructure. However, this is not something our government can do through regulation alone. Only by extensive partnering with the private sector and significant investments in technology and physical security will we adequately ensure that our economy will be protected from the risk of a physical terrorist attack.

The most dangerous threat is always the one you can’t imagine. In the cyber world, the worst threats may not come from Chinese hackers or the latest Internet virus, but rather from physical attacks against the critical infrastructure that make our connected world possible. It is time we did something about it.

Jonathan Freeman and Adam Tiffen are members of the Truman National Security Project and veterans of three tours of duty each in Iraq and Afghanistan.